In instances where the governing body does not furnish water service, but some other private or public agency furnishes water service to some or to all of the persons to whom such governing body furnishes sewer collection service, then in such event the governing body shall be fully empowered to contract with such private or public agency for the collection of its sewer service charge as a part of a single joint bill for water and sewer service. Such contract shall be upon terms and conditions mutually agreeable and shall constitute the collecting agency, the agent of the particular governing body for the purpose of collecting sewer service charges as the governing body shall from time to time impose, and shall empower the collecting agency, as agent of the governing body to disconnect water service upon nonpayment of such sewer service charge.